1. Technical Field of the Invention
The invention relates to a honeycomb, particularly a catalytic converter substrate, pursuant to the generic part of claim 1 and a process for its manufacture.
The honeycomb can consist of smooth and/or structured foils, which can be arranged in plane or curved foil layers. The honeycomb can be surrounded by a housing, in which several honeycombs can also be accommodated one behind the other or adjacent to each other, where the individual honeycombs can be partially separated by walls or supports.
2. Prior Art
Document EP 0 430 945 B1 discloses a generic honeycomb consisting of at least three stacks of foils, these being folded about an associated bending line and wrapped around the bending line. The end areas of the foils are connected to each other and/or to the housing, at least along part of the lines of contact, by jointing techniques, preferably by brazing, in order to achieve sufficient stability of the honeycomb.
Particularly when using the honeycombs as catalytic converter substrates, they are, as a result of temporal and local temperature gradients, exposed to very high stresses that, particularly as a result of the low strength of the foils and joints, lead to cracks and compression of the honeycombs at high temperatures, and thus to a changing honeycomb structure, this altering the properties of the catalytic converter. It must be borne in mind in this context that the honeycomb can easily be used at temperatures of 900xc2x0 C. and that temperatures differences within the honeycomb of 300 to 400xc2x0 C. can occur in this case. Moreover, the joining of the foils by brazing is a comparatively complex and expensive process.
The object of the invention is to create a honeycomb that is inexpensive to manufacture, displays a honeycomb structure that is sufficiently stable under the anticipated stresses, and demonstrates particularly high resistance to thermal shocks.
Due to the stiffening elements introduced according to the invention, which extend transverse to the foil layers i.e. intersect the major plane of the foil layers at an angle, for instance a 90xc2x0 angle, the honeycomb structure is sufficiently stabilised. Forces resulting from temperature changes, for example, are absorbed by the stiffening elements and no longer, or no longer exclusively, by the joints connecting the foils to each other or to the housing. The stiffening elements, which are capable of withstanding tensile forces at least in the longitudinal direction, extend across several ducts through which flow is possible. The stiffening elements can pass through the foils in this context, e.g. two or more than two, and/or at least partially surround the honeycomb on the outside and, if appropriate, extend through or around the entire honeycomb.
The stiffness of the stiffening elements can correspond to that of the foils or, given appropriate orientation, also be less than that of the foils, e.g. half the foil thickness, e.g. using appropriate wires or strips. Preferably, the stiffness in the transverse direction of the stiffening elements is significantly higher than that of the foils, but substantially lower than that of the housing. In this way, while using the same material, the thickness of the stiffening elements can be two to five times the foil thickness of the thinnest foils, possibly up to ten times the foil thickness or more. Referred to the housing, the stiffening elements can display roughly half the housing thickness, advantageously one-quarter to one-eighth of the housing thickness, or also less than this given a corresponding difference between the thicknesses of the housing and the foils. It goes without saying that, given a corresponding choice of material, the stiffness ratios do not directly correspond to the material thickness ratios. The wall thickness of the housing can thus be 0.5 to 1.5 mm, for example, and that of the foil approx. 0.02 to 0.06 mm. This thickness of the stiffening elements can be equal to the foil thickness or a multiple thereof.
If, transverse to their direction of extension, the stiffening elements are elastically deformable relative to the housing and/or mounted on the housing in elastically deformable fashion, e.g. by areas of increased flexibility or extensibility located between them, the honeycomb displays high resistance to thermal shocks and great stability, as the foils are not rigidly fastened to each other by means of the stiffening elements, there being compensation for expansion and simultaneous stabilisation instead. The elastic deformability can exist in one or both directions transverse to the direction of extension of the stiffening elements. The elastically deformable sections are advantagegeously deformable under forces acting at temperature changes between room temperature and about 600 to 1000xc2x0 C. on the honeycomb, advantageously in an extend that the tensions occurring due to the temperature changes could be absorbed significantly by the elastically deformable sections, for instance to an extend of more than 25% or more than 50%, advantageously substantially complete.
Elements of very high stiffness can also be introduced into the honeycomb, e.g. in the form of one or two-dimensional braces, the stiffness of which can be up to the stiffness of the housing or more and which are fixed to the housing indirectly or directly via elastically deformable areas. Areas of high stiffness thus alternate with the expansion areas guaranteeing the resistance to temperature shocks.
The stiffening elements according to the invention stabilise the honeycomb independently of the housing and permit relative movement of the foils in relation to the housing, this allowing optimum adaptation of the stiffness and load dissipation into the housing, on the one hand, and of the expansion properties, on the other hand, each of which have an influence on the function, stability and resistance to thermal shocks of the honeycomb. Moreover, this can also offer the option, if appropriate, of handling the honeycomb independently of the housing, e.g. when coating with catalytically active material.
The honeycombs according to the invention can, in particular, be used as catalytic converter substrates in the automotive sector, but also for other catalytic converters, e.g. in the power station sector or in chemical engineering. Accordingly, the diameter of the flow ducts can also vary over wide ranges, e.g. from approx. 1 mm to approx. 1 to 2 cm, without limitation. The flow ducts can be of one or two-dimensional design in each case.
The stiffening elements can be of one or two-dimensional design, e.g. in the form of wires, screws, strips, foils, particularly perforated foils or expanded-metal layers or the like. In this context, the stiffening elements can be of straight or curved design and extend parallel and/or perpendicular and/or at an angle to the foils forming the honeycomb structure. If appropriate, foil-type stiffening elements can also be used to divide the honeycomb structure into component honeycombs that are independent of each other in terms of flow, in which case the honeycomb continues to be a single structural unit.
The stiffening elements can be provided with meshing surfaces, such as threads, tooth profiles and the like, to form a positive connection with the respective corresponding component. In addition, the stiffening elements can also display resilient areas or plastically deformable areas extending in their longitudinal direction, these being produced by shaping or bending in each case, e.g. in the form of spiral wire springs, wire, strips of foil sections bent in meandering fashion, slitted foils or strips, expanded metal and the like.
The stiffening elements can be designed as wall sections that partially or completely pass through the honeycomb or border it on the outside as an outer wall. The wall sections can be made of downward-folded sections of the foils that are connected to each other, preferably over a large area. In this context, the sections can be connected by jointing techniques, e.g. spot welding, or in positive fashion, e.g. via braces, such as wires or the like, acting as additional stiffening elements. In particular, the sections can be folded downward in such a way that pockets arise, in which areas of other foils can be positioned, where the pockets are pressed, forming a non-positive and/or positive connection between the foils, or fastened to each other in positive fashion by means of wires. The wall sections can extend in two-dimensional manner over relatively large areas corresponding to a multiple of the diameter in each longitudinal direction, or they can also produce strip-like individual braces, for example.
In particular, the downward-folded sections can extend over the entire length of the foils.
The additional stiffening elements located within the wall sections can be designed as wires or strips. Within a wall section, the one-dimensional stiffening elements can extend parallel and/or perpendicular and/or at an angle to the individual foils. The stiffening elements that run in the plane of the wall can, if appropriate, also pass through the downward-folded sections.
The outer wall areas, in particular, can also be formed of foils laid in meandering fashion, which may also be compressed flat, where the outer walls can be arranged parallel and/or perpendicular to the foils forming the honeycomb structure. The meander-shaped areas can be passed through or surrounded by stiffening elements.
The stiffening elements can be fastened in positive, non-positive or material form to the foils or other stiffening elements, to which end the stiffening elements can pass through the respective components at a distance from their bordering edges, meaning that the stiffening elements are guided through lead-throughs that are closed on all sides. Each of the foil layers can be stabilised by corresponding stiffening elements in this way. In this context, the stiffening elements are advantageously connected to each of the foil layers which they pass through or contact, this being particularly applicable also to the one-dimensional stiffening elements. In this way, the stiffening braces can no longer simply be pulled out. In particular, the one-dimensional stiffening elements that pass through the foil layers, or other wall areas, can be hooked onto the latter in a manner capable of absorbing tensile forces, to which end the stiffening elements can be twisted in such a way that they take on a screw-like shape, forming a positive connection in the process. Alternatively, the stiffening braces can in themselves be designed to be screw-shaped. By means of a non-positive connection, foil areas folded in a V-shape can be fastened to each other, for example, to which end V-shaped folds are inserted into each other and pressed together by applying pressure. Correspondingly, one-dimensional stiffening elements can be inserted in folds of foil sections, which can also be provided on the foil ends, and pressed into these by applying pressure. Material connections can also be designed as soldered connections, e.g. brazed connections, or, in particular, also without filler material, e.g. by spot or diffusion welding.
The stiffening elements can pass through the honeycomb in an irregular, e.g. random, distribution. However, several stiffening elements are preferably provided, which are aligned parallel to each other or whose orientation in one or more directions in space changes regularly, e.g. whose coordinates differ by a constant amount in each case relative to a given reference system. The stiffening elements can thus, for example, be uniformly distributed along an arc, helical or spiral-shaped line. In this way, several stiffening elements are located on a common surface, which can be of plane or curved design, as a result of which so-called structural cells are formed by the virtual surfaces.
Moreover, several groups of stiffening elements are advantageously provided, where, as described above, the stiffening elements within a group are aligned parallel to each other or display an orientation in relation to a system of reference coordinates that differs by a predetermined amount in each case. The stiffening elements of different groups have different orientations relative to each other in this context. In this way, systems of structural cells can be created that pass through each other. As a result, given appropriate orientation of the stiffening elements, the honeycomb structure can absorb very high tensile forces in different directions and thus be optimally stabilised in accordance with the anticipated principal stress directions. Moreover, the cells of the independent cell systems can display different cell sizes and/or have different stiffening elements which, for example, differ in terms of their length, tensile strength, torsional resistance and the like.
The structural cells can extend in one or more directions in space over the entire length of the honeycomb structure and thus, for example, form honeycomb layers, or they can extend over only part of the honeycomb structure. If there are several structural cells interleaved in different manners, these can be considered as primary, secondary, tertiary cells, etc.
The stiffening elements of the structural cells can be arranged in such a way that their respective longitudinal axes run along directions in space which enclose an angle of 45xc2x0 to 120xc2x0, preferably 60xc2x0 to 90xc2x0, relative to each other, but without limitation to these angles. The longitudinal directions of the stiffening elements preferably construct a three-dimensional system. To this end, for example, the stiffening elements of a group can extend in one direction in space of a system of Cartesian, oblique or radial coordinates, for example, where two or three stiffening elements can intersect at one point or the stiffening elements are all separated from each other. Stiffening elements that only surround the honeycomb on the outside are to be included in this consideration.
In all, the formation of corresponding cell systems makes it possible to adjust the stability and, in particular, the natural oscillation behaviour of the honeycomb and its vibrational stability in accordance with the anticipated requirements.
The stiffening elements, including partition and outer walls build by folded foil sections, are preferably fixed to the housing in a manner capable of absorbing forces. For this purpose, the end areas of the foils can be angled downwards in such a way as to form outward-projecting areas. These areas can surround the honeycomb in arc-shaped or helical form over the entire length or part thereof. The outward-projecting areas can be fixed in corresponding recesses, e.g. beads, of the housing, to which end the housing can be plastically deformed, e.g. by applying torsional stress.
One essential aspect of the invention is the division of the honeycomb into component honeycombs which are vibrationally stable in themselves and, if appropriate, also independent in terms of flow, by introducing partition walls. The partition walls as well as the outer walls, for which the statements made in this application corresponding tot he partition walls holds similarly, serve simultaneously to dissipate loads into the housing wall and as expansion compensation areas. Two sides of each foil layer within the component honeycombs can be continuously connected to stiffening elements over the length of the honeycomb via singly or multiply folded sections. The folds permit transverse expansion of the partition wall areas to compensate for expansion between adjacent component honeycombs. The number and/or length of the respective bending legs permits the defined absorption of flexural and tensile stresses. Preferably, both the expansion compensation areas and the partition walls and/or outer walls are formed by folds in the foil, meaning that the wall sections are an integral part of the foils. As transitions between components with widely different material thicknesses are avoided and relative movement of the component honeycombs and the partition walls relative to the housing is possible, difference in expansion in the honeycomb structure can be uniformly absorbed in the structure.
The limitation of the individual deformation paths at the partition walls is achieved by the number of partition walls and their orientation relative to each other and to the housing wall. In this context, both the deformability of the partition walls themselves and the movement of several partition walls relative to each other can be adjusted via angled areas.
Constructing the partition and/or outer walls by connecting appropriately shaped foil areas is not only particularly cost-effective. Even with relatively small, undivided honeycombs, their indirect fastening via partition walls running parallel to the housing wall has advantages in terms of exposure to stress. It eliminates the need for complex connections of the foils to each other and to the housing. Instead, during the winding, folding or stacking process of a prefabrication stage, the honeycomb foils themselves can already be joined together separately, without a housing, to form dimensionally stable parts suitable for handling. This avoids both honeycombs that are mechanically too unstable and also those that are too rigid, e.g. produced by large-area soldering, as a result of which the limits for thermal and mechanical stresses are considerably wider.
In order to construct the partition and/or outer walls, the foils can be folded one to ten times or more, in which context it is also possible, e.g. on alternate layers, to create partition walls which are made up of foil folds that are horizontal and/or vertical relative to the foil layers. In the case of vertical folds, the multiply folded areas are essentially perpendicular to the foil layers, whereas they are essentially parallel to them in the case of horizontal folds.
In a foil system consisting of alternately smooth and structured foil layers, it is also possible for either only the structured foil layers, or only the smooth ones, to be folded in order to form partition and/or outer walls. A wide variety of different types of foil folds can readily be combined in a single honeycomb in order to achieve desired properties. The number of foil layers respectively connected to each other to form a partition wall, or the number of foil folds where individual foil layers are brought into contact with each other by compressing the foil fold, is decisive for the overall thickness of the partition wall and thus for its load-bearing capacity and stiffness. The possibility of compensating for expansion transverse to the partition walls can be varied via the fold height and the length of the bend or fold legs of the individual foil folds in the partition wall area.
The individual foil folds can already be permanently connected to each other by means of familiar jointing techniques when stacking the foils layers in order to construct the partition and/or outer walls. If the honeycomb is manufactured layer by layer, the foil folds of the topmost layer are always readily accessible and can be fastened to each other, e.g. by laterally pressing them together, or by punctiform connections or full-length connecting seams, e.g. by means of welded, bonded or adhesive connections. In particular, ceramic-coated foils can also be used in this context.
By introducing partition walls with defined expansion areas, honeycombs can be produced in which rigid and deformable areas alternate, each of which can extend over the entire cross-sectional width of the honeycomb. Thus, the honeycombs can, for example, display block-shaped, rigid areas that are produced, for example, by soldering of the individual foil layers and separated from each other by narrow deformation zones. The deformation zones can also completely surround the block-shaped areas.
If the honeycomb displays stiffening elements, such as wall areas consisting of several angled foil layer sections connected to each other via connecting points, the foil layers are advantageously fixed to the housing at a distance from the connecting points.
The angled sections can be used to construct a wall area, such as a side and/or partition wall extending over a part of the whole of the honeycomb cross-section, that is preferably essentially gas-tight or essentially prevents gas transport from the interior of the honeycomb to the housing under the conditions in which the honeycomb is used.
In order to fasten the honeycomb, each of the foil layers can, in some areas or over the entire honeycomb, be separately fixed to the housing, particularly in the area of the lateral boundary surfaces of the honeycomb. It is also possible for only one
or a few of the foil layers to be fixed to the housing in a given section of the honeycomb. The foil layers fixed to the housing can also be separated by further foil layers, where the further foil layers arranged between the fastened foil layers can be connected to the fastened layer, and thus to the housing, only via further, non-fastened foil layers or directly to the fastened layer. Each of the foil layers can, at least in some sections, also be connected both to the housing and to adjacent foil layers. The individual foil layers can each also be connected to several foil layers in a manner capable of absorbing tensile forces.
On the respective stiffening elements, which can be designed in the form of wall sections, the connecting points between the foil layers are advantageously a distance away from each other on consecutive foil layers. The connecting points are preferably designed to absorb tensile forces. A continuous connection of an internal foil layer to the housing via the connecting points, which would act as a thermal bridge, is avoided in this way. The connecting points can be a distance away from each other in a direction parallel to the foil layers, to which end the angled, interconnected sections of the foil layers can each be of a different length. Preferably, the connecting points are a distance away from each other along the height of the side wall, i.e. in a direction perpendicular to the foil layers.
A bead or a U-shaped groove can be provided on the housing for fastening the foil layers, although fastening can also be accomplished in some other suitable manner. The foil layers are preferably fastened to the housing by means of tabs folded outwards from the foil layers.
Between the areas of the honeycomb through which gas can flow and the points at which the foil layers are connected to each other, the foil layers preferably display sections with increased extensibility compared to the foil layer structure, where the direction of extension is preferably perpendicular to the wall sections. To this end, the fastening sections of the foil layer can be folded once or several times, e.g. 5 to 10 times, e.g. in V-shaped or zigzag form. In this context, the fold legs can be in close contact with each other or a slight distance apart. The length of the expansion legs can be three to twenty times the layer thickness of the foil layers or one to ten times the distance between foil layers, without limitation to these values. Given a corresponding arrangement of the connecting points between the foil layers, stiffening elements can thus be constructed, e.g. in the form of walls, which can absorb high tensile forces in one direction and display high extensibility perpendicular thereto. By appropriately folding and fastening the foil layer sections or stiffening elements, areas of increased extensibility can also be provided between areas of high tensile strength.
The foil layers are preferably connected to each other in such a way that, starting from the fastening point of the foil layers on the housing, a line extending in the direction of the inside of the honeycomb is obtained that connects the connecting points of the foil layers to each other, thus increasing the extensibility of the wall area opposite the housing.
The walls described above advantageously extend over the entire height and entire length of the honeycomb, where the walls can be of essentially gas-tight design. If feed-throughs are provided in the walls, e.g. as a result of notched fastening tabs, the feed-throughs are preferably covered in essentially gas-tight fashion by covers, so that the area of the honeycomb through which the gas flows is isolated from the housing. Separate covers or sections of adjacent foil layers can serve this purpose, to which end the length of the overlapping sections of the foil layers can be dimensioned appropriately. Moreover, only some of the foil layers can be provided with notched tabs, or the notched tabs of different foil layers are a distance apart in the direction of extension of the foil layers, so that an opening arising in a foil layer as a result of a notched tab is covered in essentially gas-tight fashion by an adjacent foil layer. The interior of the honeycomb can be provided with additional thermal insulation in this way while, at the same time, the fastening areas of the foil layers on the housing are at a lower temperature than the interior of the honeycomb, meaning that they are subjected to less material stress. A particularly good insulating effect is achieved by a multi-layer structure of the walls.
The wall constructed from overlapping foil layer sections is preferably designed in such a way that, at a temperature of approximately 900xc2x0 C. on the inside of the honeycomb and an much lower outside housing temperature (for instance of 100 to 400xc2x0 C. or lower), the fastening areas of the foil layers have a temperature of lower than approximately 500 to 600xc2x0 C. and can thus be exposed to greater mechanical stresses. To this end, the wall thickness, and thus the length of the overlapping foil layer sections forming the wall, must be selected appropriately as a function of the thickness of the foil layers. The temperature gradient obtained is additionally determined by the position of the connecting points of the individual foil layers in relation to each other.
The housing accommodating the honeycomb preferably has a double wall, such that the housing has a sandwich-like structure and displays an inner and outer housing. The inner housing preferably consists of ferritic material and the outer housing of austenitic material. The inner housing can display openings in order to fix areas of the honeycomb, e.g. notched tabs of the foil layers, or stiffening elements, such as stiffening wires, or side and partition wall areas. To this end, the inner housing can display areas capable of relative movement, between which, in the limit approach position, the areas of the honeycomb can be fixed, e.g. foil tabs or stiffening elements. To this end, the inner housing is preferably split in the transverse direction, thus producing two or more areas of the inner housing that completely surround the honeycomb and that can be moved, e.g. slid or rotated, relative to each other in the longitudinal direction in order to fasten the honeycomb. If appropriate, the inner housing can also be split longitudinally or display a parting line with a different profile. The inner housing can also display areas notched out in the form of tabs, which can particularly end at the face ends of the inner housing and which can be displaced relative to another part of the inner housing in pre-assembled condition. The area of the honeycomb fixed in the opening in the inner housing preferably reaches behind the inner housing on the side facing the outer housing, so that the area reaching behind can additionally be fixed between the inner housing and the outer housing, e.g. by a non-positive connection. When fastening the honeycomb in the housing, the honeycomb can first be fixed in the inner housing, after which the inner housing is fixed to the outer housing in a manner preventing displacement. For fastening the honeycomb in the inner housing, the latter is preferably already located in the outer housing, at least partially. The honeycomb can be fastened in that another part of the inner housing is slid into the outer housing and the fastening areas of the honeycomb are fixed, e.g. clamped, between the parts of the inner housing.
In order to manufacture a honeycomb according to the invention, layers of foils, arranged one on top of the other and ready-made in the required size, can be stacked and the corresponding foil stacks provided with stiffening elements.
Layers of foils are advantageously pre-shaped and, before or after shaping of the foil layers, stiffening elements inserted between these, the foil layers being cut off together with the stiffening elements for appropriate finishing. If appropriate, further stiffening elements can be introduced before cutting in order to fix the foil layers. The foil layers can subsequently be given the required shape and, if appropriate stabilised with further stiffening elements in this condition.
For shaping, stacked foils, e.g. alternating smooth and corrugated foil layers, can be put together to form a foil stack and laid in meandering fashion. Foils or expanded-metal layers can be inserted between the individual meandering layers as stiffening elements and, if appropriate, fixed to the foil layers by way of one-dimensional stiffening elements. The meandering foil stack formed in this way can be divided up using cutting equipment, after which the resultant pieces can be shaped into honeycombs.
When shaping the foils in order to form the honeycomb, the foils can be heated, also only in some areas, if appropriate. This is advantageous, particularly if the honeycomb consists of foils laid in zigzag fashion. To this end, it usually suffices to heat the foils only in the area of the bending points, preferably by means of resistance or induction heating. In particular, heating of the foils is also advantageous if they are pressed together with each other, or with stiffening elements, to form a non-positive connection.
The partition walls can be manufactured by the foils previously arranged one on top of the other being permanently deformed in stacks. To this end, previously preheated areas of the honeycomb can be deformed by forces applied externally to the honeycomb and acting in the longitudinal or transverse direction of the stacked layers. In this way, the foils can be folded in a single step over the entire height of the foil stack, regardless of its shape. If appropriate, the folding of the foils can be supported by exerting compressive or tensile forces acting perpendicular to the foil layers. In order to avoid undesired deformation of the foils, the corresponding sections of the honeycomb can be filled with packing material or bulk materials, such as sand.
In order to use the honeycomb as a catalytic converter substrate, the foil surface usually has to be roughened, e.g. by forming an oxide layer. The surface of the flow ducts is subsequently covered with a ceramic coating compound which either already contains the catalytically active substance or is subsequently provided with it. To this end, the definitively shaped honeycomb can be provided with an oxidic adhesion layer by heating in an oven or by resistance heating. However, pre-oxidised foil layers can also be used. Accordingly, the foil layers may already be provided with an adhesive ceramic layer even before deformation.
Advantageously, before being coated or before being installed in the housing, the honeycomb is calibrated by external compression transverse to the foil layers, in which context the duct shape and the clearance for expansion on the transversely deformable cell walls can also be set. To this end, the honeycomb can be heated to a deformation temperature, in which context it is advantageous for only individual areas of the volume of the honeycomb to be heated, e.g. individual layers. When pressure is exerted on the honeycomb in this condition, the non-heated areas are virtually not deformed at all, meaning that targeted shaping in specific areas is possible.
In particular, the honeycomb can be heated by resistance heating. Diffusion welding, high-temperature soldering or oxidation of the foil surface to increase its roughness can be carried out together with calibration.
The stiffening braces can be tensioned or re-tensioned during or after calibration.
In detail, the different variants of the honeycomb can be manufactured as follows.
In order to manufacture a honeycomb with a large number of foil layers, stacked in zigzag fashion and in part structured, a cuboid honeycomb stack can be formed by transverse folding of a longitudinally structured foil strip along perforation lines. In order to form secondary cells, wires, strips or the like are inserted between and/or through the foil layers during the folding process, depending on the specific design variant. The webs between the perforation holes are electrically contacted on both sides in the longitudinal direction and resistance-heated in order to form sharp-edged bending lines. In order to calibrate the foils, they are then electrically contacted and resistance-heated on side tabs transverse to the corrugation, the wires, strips and the like are tensioned, and the foils pressed together with lateral support. Given an appropriately set atmosphere, the process of heating for calibration provides the honeycomb with an adhesive oxide layer for the ceramic coating applied later. The shape of the calibrated honeycomb stack is then fixed by moulding and joining the outer lateral cell walls and partition walls and/or positively-fitting insertion or screw-fastening of braces before being coated with ceramic material. Individual honeycombs are then cut off, and the remaining outer cell walls or insulating walls and the housing fastening ribs moulded onto them. The honeycomb can then be joined to the fastening ribs on the housing wall.
As an alternative intermediate manufacturing step, the structured and perforated foil strip can be provided with a ceramic coating before being folded together into a foil stack. Moreover, the foil stack can be stabilised during electrically heated calibration in a vacuum by specifically applying pressure to the points of foil contact in order to form diffusion welds. Alternatively, solder joints can be formed at the points of contact during calibration by using wires or strips coated with solder material that are arranged between the foil layers, or by locally coated foils.
According to another variant, a honeycomb with housing can be manufactured as follows. A multi-layer strip stack with alternating smooth and corrugated foils is bent in meandering fashion and pre-fixed. Depending on the design variant involved, the folds with aligned meshing are produced beforehand. The introduction of bracing elements as additional cell walls fixes the curved, bent or wound stacks and connects them to inserted foils, e.g. expanded-metal foils. Pre-fixed honeycomb stacks are cut off by full-length transverse parting cuts through all layers. Following compression and moulding of compacted multi-layer folds on the foil ends, the honeycomb is compression moulded, calibrated and then joined with the cell walls. After being catalytically coated in advance, the honeycombs are fastened in the housing by means of integrally moulded external fastening ribs.
Coated or uncoated foils of alternately smooth and corrugated design can also be provided with foil folds during spiral winding and subsequently joined to form multi-layer cell walls in aligned toothed lines of defined orientation. During winding, an expanded-metal foil layer is introduced on the inside of the honeycomb and on the outer circumference and inserted in the toothed lines in the process. The honeycombs can be calibrated as described above, either with or without heating.
For transporting the honeycombs, the housing can simultaneously be used as transport packaging. In order to manufacture a catalytic converter, a tubular housing with a number of honeycombs arranged one behind the other can be divided in accordance with the size of the honeycombs. In this context, the honeycombs can be fixed to the housing wall, also regardless of the use of the housing as transport packaging, by means of ribs, e.g. spiral-shaped ribs, to which end the outward-projecting ribs can be fastened in beads provided in the tubular housing. The housing can have a single or double wall and serve to accommodate several honeycombs next to each other.
The inlet and outlet areas of the honeycomb can display foil layer sections or separate inserts with surfaces that run at an angle to the principal plane of the foil layers and improve the inflow behaviour as a whole as a result of the induced flow deflection. The foil layers are reinforced by the corresponding structuring of the foils in the turbulent inlet area. The inlet and outlet areas are advantageously reinforced by additional stiffening elements according to the invention.